Electrode, electrochemical device, and method of making electrode

ABSTRACT

An electrode comprises a planar collector, and an active material containing layer disposed on the collector. The active material containing layer comprises a plurality of particles containing an active material, and a binder for binding the particles containing the active material to each other and the particles containing the active material to the collector. The collector has a surface depressed in conformity to a form of the particles containing the active material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode usable in electrochemical devices such as primary batteries, secondary batteries (lithium-ion secondary batteries in particular), electrolytic cells, and capacitors (electrochemical capacitors in particular), an electrochemical device equipped therewith, and a method of manufacturing an electrode.

2. Related Background Art

Electrochemical devices such as high-energy batteries typified by lithium ion secondary batteries and electrochemical capacitors typified by electric double layer capacitors have widely been in use in portable devices and the like. Such an electrochemical device mainly comprises a pair of electrodes and an electrolyte (e.g., a liquid electrolyte or solid electrolyte) interposed between the electrodes.

In general, such an electrode of the electrochemical device comprises an active material containing layer stacked on a planar collector, whereas the active material containing layer includes a number of particles containing an active material. Proposed as a method of manufacturing such an electrode is one comprising the steps of preparing a kneaded product including a particle containing an active material, a binder, and a conductive auxiliary agent particle; extending the kneaded product wit a hot roller machine or hot press machine, so as to yield an active material containing sheet, and bonding the active material containing sheet to the collector (see, for example, Japanese Patent Application Laid-Open No. 2004-2105).

SUMMARY OF THE INVENTION

However, the electrode manufactured by the above-mentioned method has been found to exhibit a relatively high contact resistance between the particle containing the active material and the collector. When such an electrode is used in an electrochemical device, the internal resistance of the electrochemical device becomes higher, whereby the electrochemical device may be obstructed from achieving higher output or higher energy density.

A view of the problem mentioned above, it is an object of the present invention to provide an electrode which can filly lower the contact resistance between a particle containing an active material and a collector, an electrode equipped therewith, and a method of manufacturing the electrode.

The inventors conducted diligent studies in order to achieve the above-mentioned object and, as a result, have found the following. Namely, the conventional active material containing sheet formed by expanding a material kneaded product with a pair of rollers has a relatively smooth surface, whereby the conventional electrode comprises such an active material containing sheet having a relatively smooth surface and a planar collector bonded thereto. Therefore, the contact area between the active material containing sheet and the collector is not sufficient, whereby the contact resistance between the particle containing the active material and the collector is high.

Therefore, m one aspect, the present invention provides an electrode comprising a planar collector, and an active material containing layer disposed on the collector; wherein the active material containing layer comprises a plurality of particles containing an active material and a binder for binding the particles containing the active material to each other and the particles containing the active material to the collector, the collector having a surface depressed in conformity to a form of the particles containing the active material.

In another aspect, the present invention provides an electrochemical device comprising a pair of electrodes and an electrolyte interposed between the electrodes; wherein at least one of the pair of electrodes includes an active material containing layer comprising a plurality of particles containing an active material, and a binder for binding the particles containing the active material to each other and the particles containing the active material to the collector, the collector having a surface depressed in conformity to a form of the particles containing the active material.

In such an electrode, the collector is depressed in conformity to the form of particles containing an active material whereby the contact area between the particles containing the active material and the collector can be made larger than the conventional one. This can lower the internal resistance of the electrochemical device using such an electrode, thereby enabling the electrochemical device to raise its power and improve its energy density.

It will be preferred if the binder in the active material containing layer includes a conductive auxiliary agent particle, since a conduction path is further formed thereby between the particles containing the active material and the collector, whereby the contact resistance can further be lowered. This is also more preferable in that a conduction path is further formed between the particles containing the active material, so that the contact resistance between the particles containing the active material can be reduced, whereby the resistance of the active material containing layer itself can greatly be lowered.

Preferably, the particles containing an active material in the active material containing layer have a particle size of 0.1 to 500 μm. When the particle size of the particles containing the active material is smaller than 0.1 μm the particles containing the active material tend to flocculate and thus are less likely to disperse uniformly in the active material containing layer. When the active material containing layer includes a conductive auxiliary agent particle in particular, the contact between the particles containing the active material and the conductive auxiliary agent particle may become uneven, and the contact between the particles containing the active material, the conductive auxiliary agent particle, and the binder may become uneven, whereby problems may occur in their adhesions. When the particles containing the active material have a particle size exceeding 500 μm, on the other hand, the electrolyte and the like in the particles containing the active material tend to exhibit a greater resistance to diffuse, whereas the specific surface area of the particles containing the active material tends to become smaller. Therefore, the capacity of the electrochemical device is harder to

In still another aspect, the present invention provides a method of manufacturing an electrode, the method comprising a particle layer forming step of forming a particle layer including a binder meltable by heating and a plurality of particles containing an active material on a planar collector; and a rolling step of heating the particle layer and extending the particle layer by passing the collector and the particle layer between rotating rollers, so as to bind the particles containing the active material to each other with the binder and bind the particles containing the active material to the collector with the binder.

In the rolling step in this aspect of the present invention, the particles containing the active material are pressed against the collector, so as to dent the surface of the collector. Therefore, the electrode having a surface depressed in conformity to the form of the particles containing the active material such as the one mentioned above can be manufactured favorably. Since the forming of the active material containing layer and the binding (bonding) of the active material containing layer and collector can be carried out at the same time, the number of steps can be made smaller than that conventionally required, whereby the cost can be cut down.

When the particle layer further includes a conductive auxiliary agent particle in the particle layer forming step, the electrode whose binder includes the conductive auxiliary agent particle as mentioned above can be obtained. Such an electrode is more preferable in that it can further reduce the contact resistance between the particles containing the active material and the collector, and can also lower the contact resistance between the particles containing the active material.

Here, it will be preferred if the particle layer includes a plurality of composite particles each comprising the particles containing the active material integrated with each other beforehand by the binder including the conductive auxiliary agent particle.

This can favorably disperse the particles containing the active material and the conductive auxiliary agent particle in the composite particle beforehand Hot-rolling such a particle layer including the composite particles can form a quite favorable electronic conduction path in the active material containing layer. Therefore, the resistance of the active material containing layer can further be reduced.

It will be preferred if the rolling step is carried out by passing the collector and the particle layer between heated rollers, since this allows a single apparatus to perform the heating and rolling.

It will be preferred if a line pressure of 200×10² to 2000×10² N/m (about 20 to 200 kgf/cm) is applied between the rollers in the rolling step. When the line pressure the rollers is less than 200×10² N/n, the particles containing the active material are less likely to dent the collector sufficiently. When the line pressure of the rollers exceeds 2000×10² N/m, on the other hand, the active material containing layer is consolidated so much that the electrolyte is harder to diffuse in the active material containing layer. Accordingly, the above range of the line pressure can reduce the impedance sufficiently.

It will be preferred in the particle layer forming step if a binder layer, meltable by heating, including a conductive auxiliary agent particle is disposed beforehand on a surface of the collector, and the particle layer is formed on the binder layer.

In this case, the binder layer is also molten at the time of hot rolling, whereby the particles containing the active material and the collector can be bound to each other more favorably. Here, the particles containing the active material dent the molten binder layer, and then the collector. Since the binder layer includes the conductive auxiliary agent particle, employing such a binder layer can also sufficiently lower the contact resistance between the particles containing the active material and the collector.

It will be preferred if the particles containing the active material have a particle size of 0.1 to 500 μm. When the particle size of the particles containing the active material is smaller than 0.1 μm, the particles containing the active material tend to flocculate and thus are less likely to disperse uniformly in the active material containing layer. When the active material containing layer includes a conductive auxiliary agent particle in particular, the contact between the particles containing the active material and the conductive auxiliary agent particle may become uneven, and the contact between the particles containing the active material, the conductive auxiliary agent particle, and the binder may become uneven, whereby problems may occur in their adhesions. When the particles of the active material containing the active material have a particle size exceeding 500 μm, on the other hand, the electrolyte and the like in the particles containing the active material tend to exhibit a greater resistance to diffuse, whereas the specific surface area of the particles containing the active material tends to become smaller. Therefore, the capacity of the electrochemical device is harder to increase.

In the present invention, the “active material” refers to the following materials depending on the electrode to be formed. Namely, the “active material” refers to a reducer and an oxidizer when the electrode to be formed is an electrode wed as an anode and a cathode of a primary battery, respectively. The “particles containing the active material” can contain materials other the active material to such an extent that functions of the active material are not deteriorated thereby.

When the electrode to be formed is an anode (at the time of discharging) used in a secondary battery, the “active material” refers to a reducer, while being a material which can chemically stably exist either in its reduced or oxidized state, whereas a reducing reaction from the oxidized state to the reduced state and an oxidizing reaction from the reduced state to the oxidized state can proceed reversibly. When the electrode to be formed is a cathode (at the time of discharging) used in a secondary battery, the “active material” refers to an oxidizer, while being a material which can chemically stably exist either in its reduced or oxidized state, whereas a reducing reaction from the oxidized state to the reduced state and an oxidizing reaction from the reduced state to the oxidized state can proceed reversibly.

When the electrode to be formed is an electrode used in a primary or secondary battery, the “active material” may be a material capable of occluding or releasing metal ions involved in an electrode reaction (by intercalating/deintercalating or doping/undoping) in addition to those mentioned above. Examples of such a material include carbon materials used in anodes and/or cathodes of lithium-ion secondary batteries and metal oxides (including mixed metal oxides).

When the electrode to be formed is an electrode used in an electrolytic cell or an electrode used in a capacitor (condenser), the “active material” refers to electronically conductive metals (including metal alloys), metal oxides, and carbon materials.

The “electrolyte” in the electrochemical device in the present invention refers to (1) a porous separator formed from an insulative material and impregnated with an electrolytic solution (or a gel-like electrolyte obtained by adding a gelling agent to an electrolytic solution); (2) a solid electrolyte film (a film made of a solid polymer electrolyte or a film including an ionically conductive inorganic material); (3) a layer made of a gel-like electrolyte obtained by adding a gelling agent to an electrolytic solution; and (4) a layer made of an electrolytic solution.

The present invention can provide an electrode which can sufficiently reduce the contact resistance between a particle containing an active material and a collector, an electrochemical device equipped therewith, and a method of manufacturing the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the anode in accordance with an embodiment of the present invention;

FIG. 2 is a schematic sectional view of the cathode in accordance with an embodiment of the present invention;

FIG. 3 is a schematic sectional view showing an electrochemical device using the anode of FIG. 1 and the cathode of FIG. 2;

FIG. 4 is a schematic sectional view of a composite particle used when manufacturing an electrode;

FIG. 5 is an explanatory view showing an example of granulating step when manufacturing composite particles;

FIG. 6 is an explanatory view showing an example of rolling step when manufacturing an electrode; and

FIG. 7 is a table showing impedance values of electrochemical devices in examples A1-A4 and a comparative example A1.

FIG. 8 is a table showing impedance values of electrochemical devices in examples B1-B11.

FIG. 9 is a table showing impedance values of electrochemical devices in examples C1-C10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the present invention will be explained in detail with reference to the drawings. In the following explanations, parts identical or equivalent to each other will be referred to with numerals identical to each other without repeating their overlapping descriptions.

Anode

FIG. 1 shows a preferred embodiment of an anode 2 as an electrode for a lithium-ion secondary battery in accordance with the present invention. As shown in FIG. 1, the anode 2 comprises a planar (film-like) collector 22 and an active material containing layer 24 formed on the collector 22. The form of the anode 2 is not restricted in particular, and may be a thin film as depicted, for example.

Collector of Anode

It will be sufficient ff the collector 22 is a conductive planar material. For example, a thin metal sheet such as a copper foil can be used

Active Material Containing Layer

The active material containing layer 24 mainly comprises particles 25 containing an active material, conductive auxiliary agent particles 26, and a binder 27.

Particles Containing Active Material

Particles containing known active materials for electrochemical devices can be used as the particles 25 containing the active material. Examples of such particles 25 containing the active material include those containing carbon materials which can occlude/release lithium ions (by intercalating/deintercalating or doping/undoping), such as graphite, carbon which is hard to graphitize, carbon which is easy to graphitize, and carbon sintered at a low temperature; metals adapted to combine with lithium, such as AL, Si, and Sn; amorphous compounds mainly composed of oxides, such as SiO₂ and SnO₂; and litium titanate (Li₃Ti₅O₁₂). The particles 25 containing the active material may consist of the active material alone, or include ingredients other than the active material.

The average particle size of the particles 25 is preferably 0.1 to 500 μm. When the particle size of the particles 25 containing the active material is lower than 0.1 μm, the particles 25 containing the active material tend to flocculate and thus are less likely to disperse uniformly in the active material containing layer. When the particles 25 containing the active material have a particle size exceeding 500 μm, on the other hand, the electrolyte and the like in the particles 25 containing the active material tend to exhibit a greater resistance to diffuse. Namely, when the particle size of the particles 25 containing the active material is larger than 500 μm, ionic diffusion resistance in the particles 25 containing the active material becomes very large, and thus an impedance tends to become larger. The preferable particle size of the particles 25 containing the active material is 0.1 to 50 m.

Binder

The binder 27 binds the particles 25 containing the active material to each other such that the particles 25 containing the active material come into contact with each other, and the particles 25 containing the active material to the collector 22 such that the particles 25 containing the active material and the collector 22 come into contact with each other.

As long as the above-mentioned binding is possible, the material of the binder 27 is not limited, examples of which include fluorine resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (my), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

Examples of the binder 27 other than those mentioned above include vinylidene-fluoride-based fluorine rubbers such as vinylidene-fluoride/hexafluoropropylene-based fluorine rubber (VDF/HFP-based fluorine rubber), vinylidene-fluoride/hexafluoropropylene/tetrafluoroethylene-based fluorine rubber (VDF/HFP/TFE-based fluorine rubber), vinylidene-fluoride/pentafluoropropylene-based fluorine rubber (VDF/PFP/TFE-based fluorine rubber), vinylidene-fluoride/pentafluoropropylene/tetrafluoroethylene-based fluorine rubber (VDF/PFP/TFE-based fluorine rubber), vinylidene-fluoride/perfluoromethylvinyl-ether/tetrafluoroethylene-based fluorine rubber (VDF/PFMVE/TFE-based fluorine rubber), and vinylidene-fluoride/chlorotrifluoroethylene-based fluorine rubber (VDF/CTFE-based fluorine rubber).

Examples of the binder 27 other than those mentioned above include polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene/butadiene rubber, isoprene rubber, butadiene rubber; and ethylene/propylene rubber. Also employable are thermoplastic elastomeric polymers such as styrene/butadiene/styrene block copolymer, its hydrogenetated products, styrene/ethylene/butadiene/styrene copolymer, styrene/isoprene/styrene block copolymer, and its hydrogenated products. Further, syndiotactic 1,2-polybutadiene, ethylene/vinyl acetate copolymer, propylene-α-olefin (whose carbon number is 2 to 12) copolymers, and the like may be used.

Electronically conductive polymers and ionically conductive polymers may also be used as the binder 27. An example of the electronically conductive polymers is polyacetylene. In this case, the binder 27 also functions as a conductive auxiliary agent particle, thereby making it unnecessary to add the conductive auxiliary agent particles 26.

As the ionically conductive polymers, those exhibiting conductivity for ions such as lithium ion can be used, for instance. Examples of the ionically conductive polymers include those in which monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, crosslinked polymers of polyether compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl pyrrolidone, polyvinylidene carbonate, polyacrylonitrile, etc.) are complexed with lithium salts such as LiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiCl, LiBr, Li(CF₃SO₂)₂N, and LIN(C₂F₅SO₂)₂ or alkali metal salts mainly composed of lithium. Examples of polymerization initiators used for complexing include photopolymerization initiators and thermal polymerization initiators suitable for the above-mentioned monomers.

The content of the binder 27 included in the active material containing layer 24 is preferably 0.5 to 6 mass % based on the mass of the active material containing layer 24. When the content of the binder 27 is less than 0.5 mass %, the amount of the binder 27 is so small that the active material containing layer 24 is less likely to be formed firmly. When the content of the binder 27 exceeds 6 mass %, on the other hand, the amount of binder 27 not contributing to the electric capacity increases so much that a sufficient volume energy density is harder to attain When the electronic conductivity of the binder 27 is low in particular in this case, the electric resistance of the active material containing layer 24 rises so much that a sufficient electric capacity is harder to attain.

Conductive Auxiliary Agent Particles

The conductive auxiliary agent particles 26 are not restricted in particular, whereby known conductive auxiliary agent particles may be used. Examples of the conductive auxiliary agent particles include carbon materials such as carbon blacks, highly crystalline synthetic graphite, and natural graphite; fine powders of metals such as copper, nickel, stainless, and iron; mixtures of the above-mentioned carbon materials and fine powders of metals, and powder materials of conductive oxides such as ITO and the like. The average particle size of the conductive auxiliary agent particles is smaller than that of the particles containing the active material, preferably on the order of 1 to 500 nm.

The conductive auxiliary agent particles 26 are included in the binder 27 by a large amount. The conductive auxiliary agent particles 26 exist singly or in series between the particles 25 containing the active material or between the particles 25 containing the active material and the collector 22, thereby forming further conduction paths therebetween. This is effective in flirter lowering the contact resistance between the particles 25 containing the active material and the contact resistance between the particles 25 containing the active material and the collector 22 within the active material containing layer 24.

The content of the conductive auxiliary agent particles 26 included in the active material containing layer 24 is preferably 0.5 to 6 mass % based on the total mass of the active material containing layer 24. When the content of the conductive auxiliary agent particles 26 is less than 0.5 mass %, the amount of the conductive auxiliary agent particles 26 is so small that appropriate conduction paths are harder to be formed in the active material containing layer 24. When the content of the conductive auxiliary agent particles 26 exceeds 6 mass %/, on the other hand, the amount of conductive auxiliary agent particles 26 not contributing to the electric capacity increases so much that a sufficient volume energy density is harder to attain.

Such an active material containing layer 24 includes conduction paths in which the particles 25 containing the active material are directly in contact with each other, and conduction paths in which the particles 25 containing the active material are in contact with each other by way of one or a plurality of conductive auxiliary agent particles 26. Therefore, the particles 25 containing the active material form a three-dimensional network structure in which they are electrically connected to each other without being isolated.

Also, such an active material containing layer 24 includes conduction paths in which the particles 25 containing the active material are directly in contact with the collector 22, and conduction paths in which the particles 25 containing the active material are in contact with the collector 22 by way of one or a plurality of conductive auxiliary agent particles 26, whereby the particles 25 containing the active material are electrically connected to the collector 22 by the conduction paths.

In particular, the particles 25 containing the active material dent the surface of the collector 22 in this embodiment, so that the surface of the collector 22 is depressed in conformity to the form of the particles 25 containing the active material thus forming depressions 22 a.

Cathode

FIG. 2 shows a preferred embodiment of the cathode 3 as an electrode for the lithium-ion secondary battery in accordance with the present invention. The cathode 3 comprises a planar collector 32 and an active material containing layer 34 formed on the collector 32.

Collector of Cathode

Employable as the collector 32 are conductive planar materials, an example of which is an aluminum foil.

Active Material Containing Layer of Cathode

The active material containing layer 34 mainly comprises particles 35 containing an active material, conductive auxiliary agent particles 36, and a binder 37.

Particles Containing Active Material

The particles 35 containing the active material are not restricted in particular, whereby particles containing known active materials for electrochemical devices can be used therefor. Examples of the particles 35 containing the active material include those containing lithium cobaltate (LiCoO₂), lithium nickelate (LiNiO₂), lithium manganese spinel (LiMn₂O₄), mixed metal oxides represented by the general formula of LiNi_(x)MN_(y)Co_(z)O₂ (x +y+z =1), lithium vanadium compounds, V₂O₅, olivine-type LiMPO₄ (where M is Co, Ni, Mn, or Fe), and lithium titanate (Li₃Ti₅O₁₂). The particles 35 containing the active material may consist of the active material alone or include other materials as a matter of course.

The average panicle size of the particles 35 containing the active material is preferably 0.1 to 500 μm in the cathode 3. When the particle size of the particles 35 containing the active material is less than 0.1 μm, the particles 35 containing the active material tend to flocculate and thus are less likely to disperse uniformly in the active material containing layer. When the particles 35 containing the active material have a particle size exceeding 500 μm, on the other hand, the electrolyte and the like in the particles 35 containing the active material tend to exhibit a greater resistance to diffuse. Namely, when the particle size of the particles 35 containing the active material is larger than 500 μm, ionic diffusion resistance in the particles 35 containing the active material becomes very large, and thus an impedance tends to become larger. The preferable particle size of the particles 35 containing the active material is 0.1 to 50 μm.

Binder Conductive Auxiliary Agent etc.

As the conductive auxiliary agent particles 36 and binder 37, materials similar to the conductive auxiliary agent particles 26 and binder 27 in the active material containing layer of the anode 2 can be used in a similar mode. Operations and effects of the conductive auxiliary agent particles 36 and binder 37 are similar to those in the anode 2. Preferably, the contents of the conductive auxiliary agent particles 36 and binder 37 included in the active material containing layer 34 are made similar to those in the anode 2.

From the viewpoint of forming contact interfaces between the particles 35 containing the active material and the electrolyte three-dimensionally with a sufficient size, the BET specific surface area of the particles 35 containing the active material is preferably 0.1 to 10 m²/g, more preferably 0.1 to 5 m²/g.

The active material containing layer 34 includes conduction paths in which the particles 35 containing the active material are directly in contact with each other, and conduction paths in which the particles 35 containing the active material are in contact with each other by way of one or a plurality of conductive auxiliary agent particles 36, whereby the particles 35 containing the active material form a three dimensional network structure in which they are electrically connected to each other without being isolated

Also, such an active material containing layer 34 includes conduction paths in which the particles 35 containing the active material are directly in contact with the collector 32, and conduction paths in which the particles 35 containing the active material are in contact with the collector 32 by way of one or a plurality of conductive auxiliary agent particles 36, whereby the particles 35 containing the active material are electrically connected to the collector 32 by the conduction paths.

In particular, the particles 35 containing the active material dent the surface of the collector 32 in this embodiment, so that the surface of the collector 32 is depressed in conformity to the form of the particles 35 containing the active materials thus forming depressions 32 a.

Operations and effects of such anode 2 and cathode 3 will now be explained. In the anode 2 and cathode 3, the surfaces of the collectors 22, 32 are formed with the depressions 22 a, 32 a in conformity to the forms of the particles 25, 35 containing the active materials, whereby the particles 25, 35 containing the active materials partly fit into the depressions 22 a, 32 a, Therefore, the anode 2 and cathode 3 in this embodiment can yield wider contact areas between the particles 25, 35 containing the active material and the collectors 22, 32 than those in the conventional anode 2 and cathode 3 with no depressions. Therefore, the contact resistance between the collectors 22, 32 and the particles 25, 35 containing the active material becomes smaller. This can lower the internal resistance of the electrochemical device using the anode 2 and cathode 3, thereby allowing the electrochemical device to increase its output and improve its energy density.

Electrochemical Device

An example of the lithium-ion secondary battery 1 as an electrochemical device using the above-mentioned anode 2 and cathode 3 will now be explained

FIG. 3 is a schematic sectional view showing a basic configuration of the lithium-ion secondary battery 1 in accordance with an embodiment. The lithium-ion secondary battery 1 is mainly constituted by a unit cell 5 including the anode 2, the cathode 3, and an electrolyte layer 4 disposed between the anode 2 and cathode 3; and a case 7 sealing the unit cell 5 therein. At the time of charging, the anode 2 is connected to an anode of an external power supply (none of which is depicted), so as to function as a cathode. At the time of charging, the cathode 3 is connected to a cathode of an external power supply (none of which is depicted), so as to function as an anode.

Electrolyte Layer

The electrolyte layer 4 may be a layer made of an electrolytic solution, a solid electrolyte (ceramic solid electrolyte or solid polymer electrolyte), or a layer constituted by a separator and an electrolytic solution and/or solid electrolyte infiltrated into the separator.

The electrolytic solution is prepared by dissolving a lithium-containing electrolyte into a nonaqueous solvent. The lithium-containing electrolyte may appropriately be chosen from LiClO₄, LiBF₄, LiPF₆, and the like, for example, whereas lithium imide salts such as Li(CF₃SO₂)₂N and Li(C₂F₅SO₂)₂N, LiB(C₂O₄)₂, and the like can also be used. The nonaqueous solvent can be selected from organic solvents exemplified in Japanese Patent Application Laid-Open No. SHO 63-121260 and the like, such as ethers, ketones, and carbonates, for example. In particular, carbonates are preferably used in the present invention.

Among the carbonates, a mixed solvent mainly composed of ethylene carbonate with at least one species of other solvents added thereto is preferably used in particular. In general, the mixing ratio is preferably such that ethylene carbonate/other solvents=5 to 70:95 to 30 (volume ratio). Ethylene carbonate has a high solidifying point of 36.4° C., so that it is solidified at normal temperature and thus cannot be used alone as an electrolytic solution for a battery. When at least one species of other solvents having a lower solidifying point is added thereto, however, the mixed solvent lowers its solidifying point, so as to be usable.

As the other solvents in this case, any solvents can be used as long as they can lower the solidifying point of ethylene carbonate. Their examples include diethyl carbonate, dimethyl carbonate, propylene carbonate, 1,2-dimethoxyethane, methylethyl carbonate, γ-butyrolactone, γ-valerolactone, γ-octanoic lactone, 1,2-diethoxyethane, 1,2-ethoxymethoxyethane, 1,2-dibutoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4,4-dimethyl-1,3-dioxane, butylene carbonate, and methyl formate. Employing the above-mentioned mixed solvent while using a carbonaceous material as an active material of the anode can remarkably improve the battery capacity and fully lower the irreversible capacity ratio.

Such an electrolytic solution infiltrates into pores of the active material containing layer 24 in the anode 2 and pores of the active material containing layer 34 in the cathode 3.

An example of the solid polymer electrode is a conductive polymer having an ionic conductivity.

The above-mentioned conductive polymer, is not restricted in particular as long as it has a lithium ion conductivity. Examples of the conductive polymer include those in which monomers of polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, crosslinked polymers of polyether compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl pyrrolidone, polyvinylidene carbonate, polyacrylonitrile, etc.) are complexed with lithium salts such as LiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiCl, LiBr, Li(CF₃SO₂)₂N, and LiN(C₂F₅SO₂)₂ or alkali metal salts mainly composed of lithium. Examples of polymerization initiators used for complexing include photopolymerization initiators and thermal polymerization initiators suitable for the above-mentioned monomers.

Examples of support salts constituting the polymer solid electrolyte include salts such as LiClO₄, LiPF₆, LiBF₄, LiAsF₆, LiCF₃SO₃, LiCF₃CF₂SO₃, LiC(CF₃SO₂)₃, LiN(CF₃SO₂)₂, LiN(CF₃CF₂O₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂), and LiN(CF₃CF₂CO)₂, and their mixtures.

When using the solid electrolyte, the solid electrolyte is further added into pores of the active material containing layer 24 in the anode 2, and pores of the active material containing layer 34 in the cathode 3.

When a separator is used in the electrolyte layer 4, examples of its constituent materials include one or more species of polyolefins such as polyethylene and polypropylene (laminates of two or more layers of films and the like when two or more species can be used), polyesters such as polyethylene terephthalate, thermoplastic fluorine resins such as ethylene/tetrafuoroethylene copolymer, and celluloses. Modes of the sheet include microporous films, woven fabrics, nonwoven fabrics, and the like having a thickness of about 5 to 100 μu while exhibiting an air permeance of about 5 to 2000 sec/100 cc as measured by the method defined in JIS-P8117. Monomers of the solid electrolyte may be infiltrated into the separator and cured, so as to be polymerized for use. The above-mentioned electrolytic solution may be used as being contained in a porous separator.

The case 7 is not restricted in particular as long as it can seal the unit cell 5. For example, metal cans, resin cases, and metal laminate film packs can be used.

Since the contact resistance between the collectors 22, 32 of the anode 2 and cathode 3 and the active material containing layers 24, 34 is low as mentioned above, such a lithium-ion secondary battery 1 can reduce its DC electric resistance (impedance). This allows the lithium-ion secondary battery 1 to increase its output and improve its energy density.

Manufacturing Method

A preferred embodiment of methods of manufacturing the anode 2 and cathode 3 in accordance with the above-mentioned embodiments will now be explained.

First, in this embodiment, composite particles 250 for the anode 2 in which particles 25 containing an active material are bound to each other with a binder 27 including conductive auxiliary agent particles 26, and composite particles 350 for the cathode 3 in which particles 35 containing an active material are bound to each other with a binder 37 including conductive auxiliary agent particles 36 are made. Subsequently, a particle layer of the composite particles 250 and a particle layer of the composite particles 350 are stacked on their corresponding collectors, and then thus obtained laminates are hot-rolled.

To begin with, a granulating step of making the composite particles 250 will be explained. FIG. 4 is a schematic sectional view of the composite particles 250, 350.

The composite particle 250 is a relatively loose aggregate in which the particles 25 containing the active material are integrated with each other |by the binder 27 including a large number of conductive auxiliary agent particles 26. The binder 27 loosely binds the particles 25 containing the active material to each other. Therefore, the particles 25 containing the active material and the conductive auxiliary agent particles 26 are favorably dispersed in the composite particle 250. On the other hand, the composite particle 350 is one in which the particles 35 containing the active material are integrated with each other by the binder 37 including the conductive auxiliary agent particles 36, and thus has the same structure as with the composite particle 250.

Such composite particles 250 are formed by way of the following granulating step, for example. The granulating step will be explained more specifically with reference to FIG. 5.

The granulating step includes a material liquid preparing step of preparing a material liquid containing a binder, conductive auxiliary agent particles, and a solvent; a fluidizing step of fluidizing particles containing an active material within a fluidizing tank; and a spray-drying step of spraying the material liquid to the fluidized particles containing the active material so as to flocculate the particles containing the active material, and then eliminating the solvent from the material liquid so as to form a composite particle.

First, in the material liquid preparing step, a solvent adapted to dissolve the binder is used, so as to dissolve the binder therein. The conductive auxiliary agent particles are dispersed in thus obtained solution, so as to yield the material liquid. The solvent may be a solvent (dispersant) which can disperse the binder. The solvent adapted to dissolve the binder is not restricted in particular as long as it can dissolve the binder and disperse the conductive auxiliary agent particles. For example, N-methyl-2-pyrrolidone or N,N-dimethylformamide can be used.

Next, in the fluidizing step, gas flows are generated in the fluidizing tank 55 as shown in FIG. 5, and the particles 25 containing the active material are put into the gas flows, so as to fluidize the particles 25 containing the active material.

Subsequently, in the spray-drying step, droplets 256 of the material liquid are sprayed within the fluidizing tank 55, so as to attach to the fluidized particles 25 containing the active material, and are dried within the fluidizing tank 55 at the same time. Here, the droplets 256 cause the particles 25 containing the active material to attach to each other and flocculate, so as to be integrated into predetermined aggregates, whereas the solvent is eliminated from the droplets 256 of the material liquid, whereby the composite particles 250 are obtained.

More specifically, the fluidizing tank 55 is a container having a cylindrical form, for example, whose bottom is provided with an opening 52 for introducing a warm air (or hot air) L5 from the outside, so as to convect the panicles 25 containing the active material within the fluidizing tank 55. The side face of the fluidizing tank 55 is provided with an opening 54 for introducing the droplets 256 of the material liquid sprayed to the particles 25 containing the active material convected within the fluidizing tank 55. The droplets 256 of the material liquid including the binder 27, conductive auxiliary agent particles 26, and solvent are sprayed to the particles 25 containing the active material convected within the fluidizing tank 55.

Here, the temperature of the warm air (or hot air) is regulated, for example, such that the temperature of the atmosphere in which the particles containing the active material are placed is held at a predetermined temperature [preferably ranging from 50° C. to a temperature not greatly exceeding the melting point of the binder, more preferably ranging from 50° C. to a temperature not higher than the melting point of the binder (e.g., 200° C.)] at which the solvent can rapidly be eliminated from the droplets 256 of the material liquid, whereby the droplets 256 of the material liquid formed on the surfaces of the particles 25 containing the active material are dried substantially simultaneously with the spraying with the droplets 256 of the is material liquid. This can yield the composite particles 250 in which the particles 25 containing the active material are loosely bound to each other with the binder 27 containing the conductive auxiliary agent particles 26.

The amount of the conductive auxiliary agent particles 26 and binder 27 attached to the particles 25 containing the active material is preferably 1 to 12 mass %, more preferably 3 to 12 mass %, when expressed by the value of 100×(the mass of conductive auxiliary agent particles+the mass of binder)/(the mass of composite particles).

From the reasons mentioned above, it will be preferred if the particles 25 containing the active material in use have a particle size of 0.1 to 500 μm.

The composite particles 350 can be manufactured in the same manner as with the composite particles 250 explained above.

A preferred example of method of forming the anode 2 using thus obtained composite particles 250 will now be explained with reference to FIG. 6. The cathode 3 can be manufactured in the same manner, while using the composite particles 350.

Specifically, the method can include a particle layer forming step of supplying the collector 22 with the composite particles 250, so as to form a particle layer 210 containing the composite particles 250; and a rolling step of passing the collector 22 and particle layer 210 between rotating rollers, while heating the particle layer 210, so as to hot-roll the particle layer 210.

Such steps can easily be carried out by a hot roll press machine 300 shown in FIG. 6, for example.

Specifically, the collector 22 bridges feed rollers 302, 304 substantially horizontally. A conductive resin layer (binder layer) 22 b is formed on the upper face of the collector 22 beforehand. The conductive resin layer 22 b can contain a binder meltable by heating and conductive auxiliary agent particles. Specifically, it will be preferred if the conductive resin layer 22 b contains the binder 27 and conductive auxiliary agent particles 26 of the composite particles 250.

Subsequently, a hopper 306 storing the composite particles 250 supplies the composite particles 250 onto the conductive resin layer 22 b of the collector 22, so as to form the particle layer 210 on the collector 22. Then, the collector 22 having the particle layer 210 laminated thereon is passed between a pair of hot rollers 312, 314 rotating while being heated.

This melts the binder 27 of the composite particles 250 and consolidates the composite particles 250, thereby forming the active material containing layer 24 having the above-mentioned structure on the collector 22.

The active material containing layer 24 is formed like a single plate, and is bound to the collector 22 by the binder 27 including the conductive auxiliary agent particles 26.

Since the composite particles 250 are extended by the hot rollers 312, 314 in this embodiment, the particles 25 containing the active material are strongly pressed against the surface of the collector 22, so as to dent the collector 22, whereby the surface of the collector 22 is depressed in conformity to the form of the particles 25 containing the active material. Therefore, an electrode having the depressions 22 a and exhibiting a low contact resistance between the particles 25 containing the active material and the collector 22 can easily be manufactured as mentioned above. Also, since the forming of the sheet-like active material containing layer 24 and the bonding of the active material containing layer 24 to the collector 22 can be carried out at the same time, the number of steps can be made smaller than that conventionally required, whereby the cost can be cut down

Preferably, the surface temperature of the hot rollers 312 and 314 is 60 to 200° C. Though depending on the melting temperature of the binder 27, such a temperature range allows the binder 27 to favorably bind the particles 25 containing the active material to each other, and the particles 25 containing the active material to the collector 22. When the temperature is lower than 60° C., the binding property tends to deteriorate. When the temperature exceeds 200° C., on the other hand, it greatly exceeds the melting point or softening point of binders used in general, whereby a firm sheet is harder to make.

The line pressure applied between the hot rollers 312, 314 is preferably 200×10² to 2000×10² N/m (about 20 to 200 m kgf/cm). When the line pressure of the rollers is less than 200×10² N/n here, the particles 25 containing the active material are less likely to dent the collector 22 sufficiently. When the line pressure of the rollers exceeds 2000×10² N/n, on the other hand, the active material containing layer 24 is consolidated so much that the electrolyte is harder to diffuse within the active material containing layer 24. Accordingly, the impedance of the electrochemical devices can be sufficiently reduced by the range of 200×10² to 2000×10² N/m.

Since the composite particles 250 are used in this embodiment, the particles 25 containing the active material and the conductive auxiliary agent particles 26 can be dispersed in the composite particles 250 beforehand, whereby the particles 25 containing the active material and the conductive auxiliary agent particles 26 can attain a sufficient dispersibility in the active material containing layer 24 formed by rolling. Therefore, the particles 25 containing the active material and the conductive auxiliary agent particles 26 can form a quite favorable three-dimensional network of electronic conduction paths in the active material containing layer 24.

When the conductive resin layer 22 b is formed on the collector 22 beforehand, the adhesion of the active material containing layer 24, i.e., the particles 25 containing the active material, to the collector 22 improves remarkably. Even when the resin layer 22 b exists on the collector 22 beforehand, the hot rollers allow the particles 25 containing the active material to penetrate through the resin layer 22 b and dent the collector 22. Since the resin layer 22 b is a conductive resin layer, the contact resistance between the particles 25 containing the active material and the collector 22 can be made sufficiently low. Even if the resin layer 22 b is not formed on the collector 22 beforehand, an electrode exhibiting operations and effects of the present invention can be formed

The particle layer forming step may form the particle layer by further mixing unintegrated single particles, i.e., at least one species selected from the particles 25 containing the active material, conductive auxiliary agent particles 26, and binder 27, in addition to the composite particles 250. The electrode in accordance with this embodiment can also be made when a particle layer including unintegrated single particles, i.e., the particles 25 containing the active material, conductive auxiliary agent particles 26, and binder 27, is formed without using the composite particles 250 at all.

The particle layer 210 may be heated by an infrared lamp or the like instead of the heated hot rollers, and then passed between unheated rollers.

Thus manufactured electrode can easily be tamed into a desirable electrochemical device by a known method.

Though preferred embodiments of the present invention are explained in the foregoing, the present invention is not restricted thereto.

For example, though the conductive auxiliary agent particles 26 are added in order to improve the electric contact between the particles 25 containing the active material and/or between the particles 25 containing the active material and the collector 22, operations as an electrode are possible without the addition of the conductive auxiliary agent particles 26 when the binder 27 has a conductivity or the like or depending on characteristics of the particles 25 containing the active material or the like.

Though the above-mentioned electrochemical device comprises the electrode of the embodiment as each of the anode and cathode, it will be sufficient if the electrode of the embodiment is provided as at least one of the anode and cathode.

Though the above-mentioned electrochemical device includes one unit cell 5, a plurality of unit cells may be laminated as well. In this case, the unit cells may be connected either in parallel or in series.

Though the above-mentioned embodiment of the electrochemical device relates to a lithium-ion secondary battery, the electrochemical device in accordance with the present invention may be any of other secondary batteries and primary batteries, for example, as long as it comprises at least an anode, a cathode, and an ionically conductive electrolyte layer, while the anode and cathode oppose each other by way of the electrolyte layer. As the particles containing the active material for the active material containing layer of the anode or cathode, not only those exemplified above but those used in known primary batteries can also be employed. The conductive auxiliary agent particles and binder may be the same as the materials exemplified above.

The electrode of the present invention is not limited to electrodes for batteries, but may be an electrode used in electrolytic cells, electrochemical capacitors (electric double layer capacitors, aluminum electrolytic capacitors, etc.), or electrochemical sensors. In the case of an electrode for an electric double layer capacitor, for example, carbon materials having a high electric double layer capacity such as coconut shell activated carbon, pitch-based activated carbon, and phenol-resin-based activated carbon can be used as particles containing the active material for the active material containing layer of the anode or cathode. In the case of a double layer capacitor, the specific surface area of the particles containing the active material is preferably 500 to 3000 m²/g in each of the cathode 3 and anode 2.

For an anode used for brine electrolysis, a pyrolyzed product of ruthenium oxide (or a mixed oxide of ruthenium oxide and other metal oxides) may be used as particles containing the active material for the active material containing layer, for example.

When the electrochemical device of the present invention is an electrochemical capacitor, any of aqueous electrolytic solutions and nonaqueous electrolytic solutions (nonaqueous electrolytic solutions using organic solvents) used in known electrochemical capacitors such as electric double layer capacitors can be employed as the electrolytic solution.

Species of the nonaqueous electrolytic solutions are not restricted in particular, but are selected in view of the solubility and degree of dissociation of the solute and the viscosity of the liquid in general, and are desirably those having a high conductivity and a wide potential window. Examples of the organic solvents include propylene carbonate, diethylene carbonate, and acetonitrile. Examples of the electrolytes include quaternary ammonium salts such as tetraethylammonium tetrafluoroborate (boron tetraethylammonium tetrafluoride). In this case, the mingling moisture must be controlled strictly.

When the secondary battery 1 is a metal lithium secondary battery, its anode (not depicted) may be an electrode solely constituted by metal lithium or a lithium alloy also acting as a collector. The lithium alloy is not restricted in particular, examples of which include alloys such as Li—Al, LiSi, and LiSn (LiSi being taken as an alloy here). In this case, it will be sufficient if the cathode is constructed by composite particles 250 having a configuration which will be explained later.

EXAMPLES

In the following, the present invention will be explained in more detail with reference to examples and a comparative example, which do not restrict the present invention at all.

Example A1

First, electrodes for an electric double layer capacitor were made.

(1) Making of Composite Particles

To begin with, composite particles 250 for use in the manufacturing of active material containing layers in electrodes for the electric double layer capacitor were made by the following procedure. Here, the composite particles 250 were constituted by a cathode/anode active material (90 mass %), conductive auxiliary agent particles (5 mass %), and a binder (5 mass %).

As the cathode and the anode active material particles containing the active material), activated carbon (having an average particle size of 15 μm) was used. As the conductive auxiliary agent particles, carbon black (acetylene black) was used As the binder, polyvinylidene fluoride PVDF) was used

First, a “material liquid” (containing 3 mass % of carbon black and 2 mass % of polyvinylidene fluoride) in which carbon black was dispersed in a solution in which polyvinylidene fluoride had been dissolved in N,N-dimethylformamide acting as a solvent was prepared.

Subsequently, air flows were generated in a container having the same configuration as with the fluidizing tank 55 shown in FIG. 5, and particles of activated carbon were put therein, so as to be fluidized. Then, the above-mentioned material liquid was sprayed to the fluidized particles of activated carbon, so as to attach the solution onto surfaces of the activated carbon particles, thereby causing the particles to flocculate. The temperature in the atmosphere in which the activated carbon particles were placed was held constant at the time of spraying, so as to eliminate NN-dimethylformamide from the particle surfaces substantially simultaneously with the spraying. This yielded the composite particles 250 (having an average particle size of 200 μm) in which the activated carbon particles were bound to each other with polyvinylidene fluoride including carbon black, so as to be integrated with each other.

The respective amounts of activated carbon, carbon black, and polyvinylidene fluoride used in the granulating were regulated such that the mass ratio of these components in the finally obtained composite particles 250 became the above-mentioned value.

(2) Making of Electrodes

Subsequently, electrodes (cathode and anode) were made. To begin with, a conductive resin layer (having a thickness of 5 μm) was formed on one side of an aluminum foil (having a thickness of 20 μm) acting as a collector. The conductive resin layer was a layer (composed of 30 mass % of carbon black and 70 mass % of polyvinylidene fluoride) containing the same conductive auxiliary agent particles (carbon black) as those contained in the composite particles and the same binder (polyvinylidene fluoride) as that contained in the composite particles.

Next, using a hot roll press machine having the same configuration as that shown in FIG. 6, the composite particles manufactured above were diffused over the resin layer of the collector 22, so as to form a particle layer, and the collector with the particle layer was rolled by hot rollers at a high temperature. The rolling condition was such that the roller temperature was 180° C., and the line pressure applied between the rollers (hereinafter referred to as “roller line pressure”) was 700×10² N/m. As such, a pair of electrodes (cathode and anode) each including an active material containing layer with a thickness of 150 μm, an active material carrying amount of 45 mg/cm², and a porosity of 25 vol % were obtained.

(3) Making of Electric Double Layer Capacitor

The electrodes were opposed to each other so as to hold therebetween a separator made of cellulose, whereas the separator and the active material containing layers were impregnated with a polycarbonate solution containing 1.2 mol/L of TEMA⁺BF₄ ⁻ (triethylnethylammonium tetrafluoroborate). They were sealed into an aluminum laminate pack, so as to yield an electric double layer capacitor.

Examples A2 and A3

Examples A2 and A3 were the same as Example A1 except that the roller line pressure was 200×10² N/m and 2000×10² N/m, respectively.

Example A4

A lithium-ion secondary battery was made in Example A4. For the anode, the same electrode as that of Example Al was used. On the other hand, the cathode was made by the same hot rolling as with Example A1 while using the following composite particles and collector.

The composite particles were made as in Example A1 while using LiCoO₂ particles (having an average particle size of 0.5 mm) as particles containing the active material, acetylene black (Denka Black) as the conductive auxiliary agent particles, and polyvinylidene fluoride (PVDF) as the binder. The particle size of the composite particles was 200 μm. The composite particles were constituted by 90 mass % of the particles containing the active material, 7 mass % of the conductive auxiliary agent particles, and 3 mass % of the binder.

Employed as the collector was an aluminum foil (with a thickness of 20 μm) having a surface formed with a conductive resin layer (with a thickness of 5 μm) including 30 mass % of acetylene black and 70 mass % of polyvinylidene fluoride. An Electrolytic solution containing 1.2 mol/L of LiBF₄ as electrolyte and mixture of ethylene carbonate and propylene carbonate (70:30 by volume) as a solvent was used.

Comparative Example A1

Comparative Example A1 was the same as Example A1 except that the composite particles were hot-rolled at a roller line pressure of 700×10² N/m by hot rollers at 120° C., so as to form an active material containing sheet, then the active material containing sheet was overlaid on the collector, and they were thermo-compressed at 5 MPa at 180° C.

FIG. 7 shows DC impedance values of these electrochemical devices at 1 kHz. It was verified that Examples 1 to 4 each having formed the active material containing layer by hot-rolling the particle layer formed on the collector as in the present invention were able to lower the impedance of batteries and capacitors as compared with Comparative Example 1 which formed a sheet of the active material containing layer and then bonded it to the collector as conventionally done.

Example B1

An electric double layer capacitor of Example B1 was made under the same condition except that; the composite particles were made using activated carbon having 2 μm of particle size as the particles containing the active material (90 mass%), acetylene black as the conductive auxiliary agent particles (6 mass%), and PVDF as the binder (4 mass%), the particle size of the composite particles was ⁶⁰ μm, the rolling condition was such that the roller temperature was 120° C., and the active material carrying amount was 9.0 mg/cm².

Example B2 to B6

Example B2 was the same as Example B1 except that the particle size of the active carbon was 5 μm and the particle size of the composite particles was 120 μm. Example B3 was the same as Example B1 except that the particle size of the active carbon was 15 μm and the particle size of the composite particles was 200 μ. Example B4 was the same as Example B1 except that the particle size of the active carbon was 18 μm and the particle size of the composite particles was 300 μm. Example B5 was the same as Example B1 except that the particle size of the active carbon was 22 μm and the particle size of the composite particles was 450 μm. Example B6 was the same as Example B1 except that the particle size of the active carbon was 28 μm and the particle size of the composite particles was 580 μm.

Example B7 to B10

Example B7 was the same as Example B3 except that the roller line pressure was 150×10² N/m. Example B8 was the same as Example B3 except that the roller line pressure was 250×10² N/m. Example B9 was the same as Example B3 except that the roller line pressure was 1900×10² N/m. Example B10 was the same as Example B3 except that the roller line pressure was 2200×10² N/m.

Example B11

Example B11 was the same as Example B3 except that the electrode was made under the condition that the particle layer including unintegrated single particles, i.e., the activated carbon as the particles containing the active material, the acetylene black as conductive auxiliary agent particles, and the PVDF as binder, was formed on the collectors without using the composite particles at all.

Example C1

A Lithium ion secondary battery was made in the Example C1. The anode was the same as the Example B3. On the other hand, the cathode was made under the same condition of Example B3 except that; the following composite particles and collector were used, the active material carrying amount was 45 mg/cm², and a porosity was 28 vol %. The roller line pressure was 700×10² N/m.

The composite particles were constituted by LiCoO₂ particles (having 2 μm of particle size) as the particles containing the active material (90 mass %/o), acetylene black (Denka Black) as the conductive auxiliary agent particles (7 mass %), and the PVDF as a binder (3 mass %). The particle size of the composite particles was 60 μm.

The collector was an aluminum foil (having a thickness of 20 μm). An conductive resin layer (composed of 30 mass % of acetylene black and 70 mass % of polyvinylidene fluoride) was formed on the collector. An Electrolytic solution containing 1 mol/L of LiBF₄ as electrolyte and mixture of ethylene carbonate and propylene carbonate (70:30 by volume) as a solvent was used.

Example C2 to C5

Example C2 was the same as Example C1 except that the particle size of the LiCoO₂ particles was 5 μm and the particle size of the composite particles was 180 μm for the cathode. Example C3 was the same as Example C1 except that the particle size of the LiCoO₂ particles was 8 μm and the particle size of the composite particles was 250 μm for the cathode. Example C4 was the same as Example C1 except that the particle size of the LiCoO₂ particles was 12 μm and the particle size of the composite particles was 300 μm for the cathode. Example C5 was the same as Example C1 except that the particle size of the LiCoO₂ particles was 15 μm and the particle size of the composite particles was 420 μm for the cathode.

Example C6 to C9

Example C6 was the same as Example C2 except that the roller line pressure was 150×10² N/m for the cathode. Example C7 was the same as Example C2 except that the roller line pressure was 250×10² N/m for the cathode. Example C8 was the same as Example C2 except that the roller line pressure was 1800×10² N/m for the cathode. Example C9 was the same as Example C2 except that the roller line pressure was 2200×10² N/m for the cathode.

Example C10

Example C10 was the same as Example C2 except that the electrode was made under the condition that the particle layer including unintegrated single particles, i.e., the LiCoO₂ particles as the particles containing the active material, the acetylene black as conductive auxiliary agent particles, and the PVDF as binder, was formed on the collectors without using the composite particles at all.

The electric double layer capacitors of Examples B1 to D11 and the Lithium ion secondary batteries of Examples C1 to C10 had sufficient low impedance even at relatively low roller line pressure, for example, about 700×10² N/m (see FIG. 8 and FIG. 9). The preferable roller line pressure seems to be in range of 200×10² to 2000×10² N/m. It was found that, when the particle size of the particles containing the active material increase, the impedance tends to become increase.

It was also found that, when the composite particles were used to form the particle layer on the collector, the impedance tends to become decrease in contrast to the case without using the composite particles. 

1. An electrode comprising a planar collector, and an active material containing layer disposed on the collector; wherein the active material containing layer comprises a plurality of particles containing an active material, and a binder for binding the particles containing the active material to each other and the particles containing the active material to the collector, the collector having a surface depressed in conformity to a form of the particles containing the active material.
 2. The electrode according to claim 1, wherein a conductive auxiliary agent particle is contained in the binder in the active material containing layer.
 3. The electrode according to claim 1, wherein the particles containing the active material in the active material containing layer have a particle size of 0.1 to 500 μm.
 4. An electrochemical device comprising a pair of electrodes and an electrolyte interposed between the electrodes; wherein at least one of the pair of electrodes includes a planar collector, and an active material containing layer disposed on the collector; and wherein the active material containing layer comprises a plurality of particles containing an active material, and a binder for binding the particles containing the active material to each other and the particles containing the active material to the collector, the collector having a surface depressed in conformity to a form of the particles containing the active material.
 5. A method of manufacturing an electrode, the method comprising: a particle layer forming step of forming a particle layer including a binder meltable by heating and a plurality of particles containing an active material on a planar collector, and a rolling step of heating the particle layer and extending the particle layer by passing the collector and the particle layer between rotating rollers, so as to bind the particles containing the active material to each other with the binder and bind the particles containing the active material to the collector with the binder.
 6. The method of manufacturing an electrode according to claim 5, wherein the particle layer further includes a conductive auxiliary agent particle.
 7. The method of manufacturing an electrode according to claim 6, wherein the particle layer includes a plurality of composite particles each comprising the particles containing the active material integrated with each other beforehand by the binder including the conductive auxiliary agent particle.
 8. The method of manufacturing an electrode according to one of claim 5, wherein the rolling step is carried out by passing the collector and particle layer between heated rollers.
 9. The method of manufacturing an electrode according to one of claim 5, wherein a line pressure of 200×10² to 2000×10² N/m is applied between the rollers in the rolling step.
 10. The method of manufacturing an electrode according to one of claim 5, wherein, in the particle layer forming step, a binder layer, meltable by heating, including a conductive auxiliary agent particle is disposed beforehand on a surface of the collector, and the particle layer is formed on the binder layer.
 11. The method of manufacturing an electrode according to one of claim 5, wherein the particles containing the active material have a particle size of 0.1 to 500 μm. 